1. Field of the Invention
This invention relates to coprocessed (coprecipitated) combinations of at least one galactomannan (preferably locust bean gum) and at least one glucomannan (preferably konjac). In a further embodiment, the inventive galactomannan-glucomannan coprecipitate may be mixed with a gelling agent (preferably a carrageenan) to form a complex hydrogel. Both the coprecipitate and the complex hydrogel may be used as bases in water dessert gels and other foods.
2. Description of the Related Art
Land plant-derived polymannan gums (galactomannans or glucomannans) such as locust bean gum (LBG) or konjac gum are known for use by themselves or in combination with hydrocolloids such as agar, carrageenan, and xanthan gum to form gels of various textures which are used, for example, in the food industry. Of particular note are carrageenan-based systems conventionally prepared by simply admixing purified or crude carrageenan-reactive polymannan gum with a carrageenan gelling agent, especially kappa carrageenan, to provide gels widely used as thickeners or gelling agents for prepared foods. Both the single-system and mixed-system gels have other interesting and useful properties including water-binding capacity and the ability to stabilize polyphase systems such as emulsions and suspensions.
Highly-refined mixed gel systems of known types intended for use in demanding food applications such as water-based dessert gels, are commercially dependent upon convenient and economical extraction/purification/clarification techniques for obtaining a polymannan gum component substantially free of impurities, and upon good interreaction of the product with the selected gelling agent to produce clear, stable gels. Accordingly, a popular commercial water gel dessert system is one based on clarified LBG (cLBG) and carrageenan. LBG is readily clarified by extracting the water-soluble locust bean gum from its source, usually at elevated temperatures, into aqueous medium, followed by filtration and precipitation of the extract; the cLBG is then admixed with carrageenan, typically kappa carrageenan, with which it interreacts quite well. The interreacted gum enhances the strength of the resulting gel, so that the desired gelling or suspending effect of the product can be obtained with significantly less carrageenan ingredient than would be required if the carrageenan were to be used alone.
Galactomannan-based gel systems have their limitations, however. Typically, cLBG or other clarified galactomannan gum is dried and ground for storage after final recovery from the purification solution; the dried gum is then resolubilized for use. Since dried LBG and some other galactomannans commonly used in these systems are not readily soluble in cold water (see, e.g., U.S. Pat. No. 3,808,195), the aqueous solubilizing medium must be heated to above ambient temperatures (above about 25.degree. C.) to completely solubilize the dried gums and obtain full benefit of their properties, particularly viscosity modification and reactivity with gelling agents such as carrageenan. In the case of LBG, heating to at least about 60.degree. C., typically to about 80.degree. C. or more, is necessary to substantially solubilize the dehydrated purified gum for use. Otherwise, the gum fails to fully dissolve in aqueous medium, the resulting heterogeneous mixture becomes hazy on standing, and the product cannot be used where clear gels are desired. Further, optimum thickening properties of the partially solubilized gum are not realized, and reactivity is lower than with fully solubilized gum.
The use of glucomannans for applications requiring highly refined gel products is also limited. For example, konjac (Amorphophallus rivieri, A. konjac) is a known viscosity modifier for foods, and is also known to be interreactive with carrageenan to provide an improved mixed gel system. However, its use is substantially limited to applications which do not require extensive purification of crude konjac flour. Processing of the konjac flour to substantially remove impurities, particularly the proteinaceous material (sacs) encapsulating the glucomannan polymers as well as starch, odor and color, requires heating, which tends to deacetylate the poiysaccharide gum (especially in the slightly alkaline medium which improves product gel strength). The deacetylated gum will form a gel upon cooling which does not reliquefy with heating. While this is an advantage in some food uses, for example in the production of retort-resistant foods such as traditional "konyaku" noodles, as a practical matter it precludes the use of konjac in applications requiring clear, thermoreversible gels, a frequent requirement in the food industry. Additionally, owing to its high viscosity and cellular contaminants, the purified gum, whether or not substantially deacetylated, is difficult to filter and recover. It should be noted, however, that filtration is optional where the end use of the gel does not have to be clear; thus filtration can be omitted where cost or operating efficiency is an important factor.
Both glucomannans and galactomannans are well-known, and widely used either separately or in combinations thereof as thickeners, viscosifiers, or gelling agents, particularly in the food industry. As noted above, the concept of admixing landplant-derived polymannans with each other or with seaplant-derived hydrocolloids such as carrageenan or agarose to obtain mixed gel systems having advantageous properties is known: see, for example U.S. Pat. No. 2,466,146 (1949) to Baker, describing edible gelling compositions comprising Irish moss extract and locust bean gum; Lebensmittel Wissenschaften und Technologies 11:279-282 (1978) directed to carrageenan/carob gels; Food Hydrocolloids 6:199-222 (1992) and Gums and Stabilizers of the Food Industry 5, Phillips, et al., eds, Oxford Univ. Press, Oxford, England, 563-569 (1989), describing konjac glucomannan and kappa-carrageenan compositions; J App. Phycol. 4:347-351 (1992) reporting properties of compositions of seaweed extracts including kappa carrageenan and furcelleran with either konjac flour or locust bean gum; U.S. Pat. No. 5,213,834 (1993) relating to compositions of konjac glucomannan and binders such as locust bean gum and/or carrageenan with organic acid microcapsules; U.S. Pat. No. 4,427,704 (1984) to Cheney, et al., referring to konjac/carrageenan compositions; Sen-1 Gakkaishi 48:437-440 (1992) comparing konjac mannan and hydroxypropylcellulose blends; and U.S. Pat. No. 4,952,686 to Renn, et al., (1990) referring to alloys of cassia (galactomannan) gum with one or more non-glucomannan thickening or gelling agents selected from a group including locust bean gum and carrageenan, but not konjac.